linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Fix aligned pages in calculate_psi_aligned

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Message-ID: <66e0f183-83ca-428d-af53-0fac69af7d42@linux.intel.com>
Date: Tue, 9 Jul 2024 10:53:51 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Kevin Tian <kevin.tian@...el.com>,
 Louis Maliyam <louispm@...gle.com>
Cc: baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Fix aligned pages in
 calculate_psi_aligned_address()

On 7/8/24 8:14 PM, Lu Baolu wrote:
> The helper calculate_psi_aligned_address() is used to convert an arbitrary
> range into a size-aligned one.
> 
> The aligned_pages variable is calculated from input start and end, but is
> not adjusted when the start pfn is not aligned and the mask is adjusted,
> which results in an incorrect number of pages returned.
> 
> The number of pages is used by qi_flush_piotlb() to flush caches for the
> first-stage translation. With the wrong number of pages, the cache is not
> synchronized, leading to inconsistencies in some cases.
> 
> Fixes: c4d27ffaa8eb ("iommu/vt-d: Add cache tag invalidation helpers")
> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
> ---
>   drivers/iommu/intel/cache.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/iommu/intel/cache.c b/drivers/iommu/intel/cache.c
> index e8418cdd8331..113834742107 100644
> --- a/drivers/iommu/intel/cache.c
> +++ b/drivers/iommu/intel/cache.c
> @@ -246,6 +246,7 @@ static unsigned long calculate_psi_aligned_address(unsigned long start,
>   		 */
>   		shared_bits = ~(pfn ^ end_pfn) & ~bitmask;
>   		mask = shared_bits ? __ffs(shared_bits) : BITS_PER_LONG;
> +		aligned_pages = 1UL << mask;

Hmm, it appears that if mask is equal to BITS_PER_LONG (which is
typically 64), the left shift operation will overflow.

So perhaps we need another line of change:

diff --git a/drivers/iommu/intel/cache.c b/drivers/iommu/intel/cache.c
index 113834742107..44e92638c0cd 100644
--- a/drivers/iommu/intel/cache.c
+++ b/drivers/iommu/intel/cache.c
@@ -245,7 +245,7 @@ static unsigned long 
calculate_psi_aligned_address(unsigned long start,
                  * shared_bits are all equal in both pfn and end_pfn.
                  */
                 shared_bits = ~(pfn ^ end_pfn) & ~bitmask;
-               mask = shared_bits ? __ffs(shared_bits) : BITS_PER_LONG;
+               mask = shared_bits ? __ffs(shared_bits) : 
MAX_AGAW_PFN_WIDTH;
                 aligned_pages = 1UL << mask;
         }

I will make above another fix as it already causes overflow in another
path.

Kevin, sound good to you?

Thanks,
baolu